1) to irritate or torment someone.

not said as "her ass"
"her ass" is what you put a skirt on.

In RTS games such as Warcraft3, it is to continuuously do hit and run attacks until the enemy begins to speak in a colourful language. However this can only be done if you have the upper hand, or when you know the army is away from base.

redneck's version of her ass

Some would spell this in two words Her Ass

Gay slang term for a sexual act that involves the knuckles but does not include the entire fist.